1. Field of the Invention
The invention relates to a method for adjusting an injection behavior of injectors in an internal combustion engine, an engine control unit implementing the method, as well as a system for adjusting an injection behavior of injectors.
2. Description of the Related Art
Methods for adjusting an injection behavior of injectors in an internal combustion engine are known. These prior art methods share on underlying problem in that injectors for injecting fuel into cylinders of the internal combustion engine having identical control, in particular for energizing, display manufacturing-related variances in their opening behavior. If therefore, injectors of an internal combustion engine with identical flow-parameters, in particular with an identical flow-duration are controlled in the same way, they nevertheless inject different fuel amounts into the individual cylinders. With small injection amounts the variance is so significant that some injectors inject fuel into the cylinders that are allocated to them while others do not open. Pre-injection and after-injection are therefore not feasible if the injectors vary strongly. It is therefore desirable to reduce the variance of the injectors upon opening if possible, in order to improve the operation of the internal combustion engine.
German Disclosure document DE 100 55 192 A1 discloses a method for concentricity control for diesel engines with the assistance of which corrective factors for injection amounts are achieved for equalization of the individual cylinders in regard to their rotational speed proportions. This reference discloses determination of a one-time impulse response spectrum for each cylinder, whereby the cylinders are turned off individually in succession, and whereby the rotational speed is recorded above the crank angle. Moreover, the rotational speed progression of the healthy engine, that is when all cylinders operate normally, is measured. By calculating the difference of the curve progression of the healthy engine and the curve progressions for individually turned off cylinders, new curves are created which reflect the influence of each cylinder on the overall rotational speed progression. These response curves are subjected to a Fourier factorization analysis. Then the low frequency oscillations, in particular of the 0.05th to third order are considered, and associated spectral impulse responses of the individual cylinders and the individual orders of the harmonic component are captured in a matrix. During operation of the engine the rotational speed progression of the crankshaft is continuously plotted over the angle and Fourier transformed. The Fourier coefficients, preferably those of the low frequency oscillations, in particular of the harmonic component of the 0.05th to third order are summarized as a vector. Correction values for the injectors are determined in that the thus obtained vector, and is subject to a scalar multiplication with the matrix representing the impulse responses.
The present inventors found that the method of the aforementioned reference was substantially based on the assumption that the basis vectors assigned to the harmonic components of the Fourier transformation are linearly independent of each other, so that they form an orthogonal basis of a vector space. Practical experience showed however, that this assumption is not applicable, whereby the applicable vectors are positioned at least partially collinear or at least not orthogonal relative to each other. The method of the aforementioned reference can therefore not be implemented reliably with the desired results.
What is needed in the art is a method which safely and efficiently provides injector equalization, so that a series variance can be compensated for. The method must be to be simple and cost effective and should be accomplished during running operation of the internal combustion engine. It is further needed in the art to provide an engine control unit with the assistance of which the method can be implemented. Finally, a system is needed with which the injection behavior of injectors in an internal combustion engine may be adjusted.